simplify: Avoid early termination of passes due to error_goal

In large meshes with complex topology we occasionally hit a case where error_goal cutoff is not monotonic: a previous pass would simplify up to a certain goal, but a subsequent pass would arrive at a smaller goal (for example as invalid collapses get eliminated) and hit it before an error that it already encountered. If we already collapsed an edge with a given error it is always correct to collapse other edges with a smaller error. This change tweaks the conditional, which results in fewer passes on some meshes (eg thai_buddha gets ~10% faster to simplify), 2-3% smaller error on some meshes, and occasionally 1-2% larger error; most meshes simplify as they did before however.

Author: zeux

src/simplifier.cpp

@@ -1129,7 +1129,7 @@ static size_t performEdgeCollapses(unsigned int* collapse_remap, unsigned char*
 
 // on average, each collapse is expected to lock 6 other collapses; to avoid degenerate passes on meshes with odd
 // topology, we only abort if we got over 1/6 collapses accordingly.
-if (c.error > error_goal && triangle_collapses > triangle_collapse_goal / 6)
+if (c.error > error_goal && c.error > result_error && triangle_collapses > triangle_collapse_goal / 6)
 {
 TRACESTATS(6);
 break;